Detection by northern analysis of alpha 1-adrenergic receptor gene transcripts in the rat

In Northern blots of total cellular and poly(A+) RNA isolated from rat liver, renal cortex, spleen, and brain probed with a full-length cDNA encoding the hamster alpha 1-adrenergic receptor, hybridization was observed to two distinct mRNAs, at approximately 3.3 kb and approximately 2.7 kb. Only the approximately 2.7 kb mRNA species was visualized in Northern blots of total cellular and poly(A+) RNA isolated from cardiac ventricular muscle. From screening a rat heart cDNA library with the full-length hamster alpha 1-adrenergic receptor cDNA, a 632 base pair cDNA was isolated. Based upon its high degree of identity, 86% at the nucleotide level, with the hamster alpha 1-adrenergic receptor cDNA, this cDNA was considered to include the 3' end of the rat alpha 1-adrenergic receptor. When used as a probe in Northern blots of liver RNA, both the approximately 3.3 kb and approximately 2.7 kb mRNAs were visualized. Both mRNA species were expressed in fetal as well as adult liver, but steady-state levels of each gene transcript were approximately 3-fold higher in adult compared to fetal liver. Finally, results from Southern analysis of restriction enzyme fragments of genomic DNA suggest that the two gene transcripts may be products of a single gene.

Specific binding sites for prohormone atrial natriuretic peptides 1-30, 31-67 and 99-126

Two peptides with vasodilatory properties consisting of amino acids 1-30 and 31-67 of the 98 a.a. N-terminal end of the prohormone of atrial natriuretic factor (proANF) which circulates in man were investigated to determine if they have specific binding sites on membranes isolated from DDT1 MF-2 smooth muscle cells. Smooth muscle is a known biologic target of these peptides. Competitive binding experiments revealed that proANFs (1-30), (31-67), and (99-126) (i.e., C-terminus; ANF) each had specific and separate binding sites. The dissociation constants for proANFs (1-30), (31-67), and (99-126) binding were 0.11 nM, 4 nM, and 7.3 nM, respectively. The binding site concentrations for proANFs (1-30), (31-67), and ANF were 2.57, 59.91 and 40 fmols/10(6) cells, respectively. The number of binding sites per cell were 1548, 36,087, and 24,090, respectively, for proANFs (1-30), (31-67), and (99-126) (ANF). Each peptide bound to DDT1 MF-2 membranes between 10(-8) to 10(-11) M but could only bind to the other peptides' receptors at concentrations of 10(-6) and 10(-7)M. These results suggest that proANF(1-30) and proANF(31-67) do not work through the ANF receptor but rather have their own separate and distinct receptors that mediate their biologic effects.

Induction of V2 receptors in renal medulla of homozygous Brattleboro rats by arginine vasopressin

Homozygous Brattleboro rats display pronounced diabetes insipidus and when treated continuously with arginine vasopressin (AVP) acquire the ability to produce concentrated urine. In this study, the effects of continual AVP replacement on the pharmacological properties of the renal medullary V2 receptor and coupling to adenylate cyclase were examined. Osmotic minipumps that delivered AVP at four different rates were implanted into male homozygous Brattleboro rats. At the end of the 14 day treatment period, urine osmolalities were 280 +/- 24, 474 +/- 105, 1777 +/- 304 and 2202 +/- 175 mOsm/kg H2O for the 0, 31.25, 62.5 and 125 ng/hr treatment groups, respectively. Plasma AVP levels were below the level of detection for the 0 and 31.25 ng/hr treatment groups, and were 2.5 +/- 0.5 and 6.5 +/- 1.8 pg/ml for the 62.5 and 125 ng/hr treatment groups. Saturation experiments using [3H] AVP and renal medullary membranes revealed binding site concentrations of 57 +/- 9, 84 +/- 23, 164 +/- 17 and 150 +/- 18 fmol/mg protein for the 0, 31.25, 62.5 and 125 ng/hr treatment groups, respectively. AVP-stimulated cyclic AMP accumulation was enhanced in renal medullary membranes prepared from the 62.5 and 125 ng/hr treatment groups when compared to that in the 0 and 31.25 ng/hr treatment groups. From these results, it appears that circulating AVP is necessary for expression of functional V2 receptors in the homozygous Brattleboro rat renal medulla.

Circadian variation of epidermal growth factor receptor in mouse liver

The liver undergoes a biochemical and morphological circadian transformation. In this paper, we document circadian variation in the binding parameters of the hepatic epidermal growth factor receptor (EGFR). Liver membranes were prepared from ad libitum fed or fasted male CD2F1 mice killed at different circadian phases at 4 h intervals. Bmax (maximum binding) and Kd (dissociation constant) varied in a rhythmic fashion. The range of change for Bmax along the 24 h time scale was 423%. For Kd, it was 162%. Both peaked late in the dark span, and decreased late in the light span. Fasting and EGF treatment reduced Bmax and the amplitude of circadian variation.

Direct identification of the rat hepatocyte arginine8 vasopressin receptor with a radiolabelled V1-selective antagonist

We compared [3H] arginine8 vasopressin (AVP) and [3H] 1-beta-mercapto-beta, beta-cyclopentamethylene propionic acid, O-methyl tyrosine2, arginine8 vasopressin (d(CH2)5 Tyr(Me)AVP), a selective V1 receptor antagonist, as radioligands for the rat hepatocyte V1 receptor. Both radioligands bound with high affinity to a site in partially purified membranes prepared from Long Evans rat hepatocytes. The binding site concentrations obtained with either radioligand, 608 +/- 101 fmol/mg protein (n = 5) with [3H] AVP and 603 +/- 62 fmol/mg protein (n = 5) with [3H]d(CH2)5 Tyr(Me)AVP, were not significantly (p greater than 0.5) different. Furthermore, the rank order of potency of a series of synthetic vasopressin analogs and related peptides were identical in competition studies using either radioligand and were consistent with a V1 receptor interaction. Our results demonstrate that [3H] d(CH2)5 Tyr(Me)AVP is a suitable radioligand to study the V1 receptor subtype.

Plasma levels of immunoreactive mesotocin and vasotocin during oviposition in chickens: relationship to oxytocic action of the peptides in vitro and peptide interaction with myometrial membrane binding sites

Plasma concentrations of immunoreactive vasotocin (AVT) and mesotocin (MT) were measured periodically before and subsequent to spontaneous oviposition in conscious chickens. The concentrations of AVT and MT approximately an hour prior to oviposition were 5.2 +/- 1.1 microU/ml and 14.7 +/- 5.1 pg/ml, respectively. Plasma AVT levels increased abruptly at oviposition (25.1 +/- 3.3 microU/ml) and decreased to 5.0 +/- 0.6 microU/ml within 30 min postoviposition. Significant changes in MT were not observed. The data indicate that AVT is selectively released during oviposition. The uterus was removed immediately after oviposition and the oxytocic potencies of several peptides were tested on muscle strips in vitro. The order of oxytocic potencies was AVT greater than or equal to arginine vasopressin (AVP) much greater than MT = pressinoic acid. Partially purified membranes were prepared from separate portions of the uteri used in the oxytocic assay. [3H]arginine8 vasopressin, [3H]AVP, bound to membranes saturably (Bmax = 17 fmol/mg protein) and with high affinity (Kd = 0.7 nM). The rank order of potency of the peptides in displacing [3H]AVP from the binding sites was the same as in the oxytocic assay which suggests that the [3H]AVP binding sites in uterine membranes represent physiological receptors that interact with AVT during oviposition.

Role of a guanine nucleotide-binding protein in alpha 1-adrenergic receptor-mediated Ca2+ mobilization in DDT1 MF-2 cells

In this study the mechanisms involved in alpha 1-adrenergic receptor-mediated Ca2+ mobilization at the level of the plasma membrane were investigated. Stimulation of 45Ca2+ efflux from saponin-permeabilized DDT1 MF-2 cells was observed with the addition of either the alpha 1-adrenergic agonist phenylephrine and guanosine-5'-triphosphate or the nonhydrolyzable guanine nucleotide guanylyl-imidodiphosphate. In the presence of [32P]NAD, pertussis toxin was found to catalyze ADP-ribosylation of a Mr = 40,500 (n = 8) peptide in membranes prepared from DDT1 MF-2 cells, possibly the alpha-subunit of Ni. However, stimulation of unidirectional 45Ca2+ efflux by phenylephrine was not affected by previous treatment of cells with 100 ng/ml pertussis toxin. These data suggest that the putative guanine nucleotide-binding protein which couples the alpha 1-adrenergic receptor to Ca2+ mobilization in DDT1 MF-2 cells is not a pertussis toxin substrate and may possibly be an additional member of the guanine nucleotide binding protein family.

Glucocorticoid induction of beta-adrenergic receptors in the DDT1 MF-2 smooth muscle cell line involves synthesis of new receptor

We have shown that glucocorticoids induce the appearance of beta 2-adrenergic receptors in membranes of the ductus deferens smooth muscle cell line (DDT1 MF-2). A concomitant increase in isoproterenol stimulated adenylate cyclase activity in the absence of exogenously applied GTP was observed as was a significantly increased (p less than 0.05) sensitivity of the adenylate cyclase system to exogenously applied GTP. However, no significant difference in the maximal velocity of adenylate cyclase between control and steroid treatment was measurable in the presence of sodium fluoride. Induction of beta 2-adrenergic receptors in DDT1 MF-2 cells is correlated with the presence of steroid receptors (androgen and glucocorticoid) in the cells since estrogens and progesterones had no effect on receptor levels. Finally, utilizing dense amino acid labeling of cells to measure old versus newly synthesized receptor sites by a density shift method, we have documented that glucocorticoid induction of beta 2-adrenergic receptors involves synthesis of new receptor protein.

Affinity labeling of the DDT1 MF-2 cell alpha 1-adrenergic receptor with [3H]phenoxybenzamine

In this study, we used phenoxybenzamine to label the alpha 1-adrenergic receptor of a smooth muscle cell line. Our results demonstrate a dose-dependent occupancy of alpha 1-adrenergic receptors by phenoxybenzamine determined by competition for the [3H]prazosin binding site. Following incorporation of [3H]phenoxybenzamine, partially purified membranes were solubilized and subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis under reducing conditions. Despite numerous Coomassie blue-stained bands, only three bands, Mr = 80,000 +/- 500, Mr = 33,000 +/- 2,000, and Mr = 21,000 +/- 400 (N = 4), were labeled with [3H]phenoxybenzamine as determined by autofluorography. Incorporation of [3H]phenoxybenzamine into the Mr = 80,000 band, but not the Mr = 33,000 and Mr = 21,000 bands, was affected by adrenergic agonists and antagonists in a manner consistent with an alpha 1-adrenergic interaction. Labeling of the Mr = 33,000 and Mr = 21,000 bands was partially blocked by phenoxybenzamine. We conclude that [3H]phenoxybenzamine can be used as an affinity probe for the alpha 1-adrenergic receptor and that the ligand binding site of the alpha 1-adrenergic receptor resides in a Mr = 80,000 protein.

Regulation of (3H) arginine8 vasopressin binding to the rat renal medulla by guanine nucleotides

In rat renal medullary membranes, we have examined modulatory effects of guanine nucleotides on binding of arginine8 vasopressin (AVP) to its receptor. Equilibrium binding studies analyzed by an iterative curve fitting program revealed an interaction of (3H) AVP with a single class of binding sites with a dissociation constant of 1.4 +/- 0.2 nM and a binding site concentration of 201 +/- 37 fmol/mg protein (n = 6). With the addition of 100 microM guanylyl-imidodiphosphate (Gpp(NH)p), the binding site concentration was significantly (p less than 0.01) reduced to 151 +/- 36 fmol/mg protein with no change in receptor affinity. The nonhydrolyzable analogues, guanosine-5'-0-(3-thiophosphate) and Gpp(NH)p were the most potent inhibitors of (3H) AVP binding. Guanosine 5'-triphosphate and guanosine-5'-diphosphate were both relatively poor inhibitors. Guanosine-5'-monophosphate and adenosine 5'-triphosphate did not inhibit (3H) AVP binding at concentrations up to 100 microM. Furthermore, 100 microM Gpp(NH)p accelerated the dissociation of (3H) AVP from the receptor. We conclude that guanine nucleotides are important modulators of AVP binding to the V2 receptor subtype in the renal medulla.

Glucocorticoids induce a 29 000 Mr protein in DDT1 MF-2 smooth muscle cells but not in the DDT1 MF-2 GR glucocorticoid resistant variant

We have demonstrated that glucocorticoids induce in DDT1 MF-2 cells by a glucocorticoid mediated mechanism the synthesis of a methionine-cysteine rich protein of 29 000 Mr (p29). Induction of p29 is not observed in DDT1 MF-2 GR glucocorticoid resistant variants which have only 7% of glucocorticoid receptor site per cell compared to wild type cells. Increased synthesis of p29 is specific to glucocorticoids since neither androgens, estrogens, progesterone nor the glucocorticoid antagonist dexamethasone mesylate are effective inducers. Stimulation of p29 synthesis in wild type cells is observed at 10(-10) M triamcinolone acetonide, reaching a maximum at a concentration of 1 X 10(-8) M. The induction of p29 is not a function of glucocorticoid arrest of DDT1 MF-2 cells since DDT1 MF-2 cells promoted to re-enter the cell cycle by 50 ng/ml platelet derived growth factor (PDGF) continue synthesis of p29. Finally, increased levels of p29 translation products are observed in cell free translation assays carried out utilizing poly A+ RNA transcripts isolated from glucocorticoid treated cells. These data suggest that the glucocorticoid stimulation of p29 synthesis is a transcriptional and/or RNA processing event controlled by glucocorticoid receptor complexes.

Photoaffinity labeling of the DDT1 MF-2 cell alpha 1-adrenergic receptor

In this study, we have used an alpha 1-adrenergic receptor photoaffinity ligand, 2-[4-(4-azido-3-iodo-benzoyl)-piperazin-1-yl]-4-amino-6, 7-dimethoxyquinazoline (125I-APD), to label covalently the alpha 1-adrenergic receptor in a smooth muscle cell line. Our results indicate that in the absence of light, (125I)APD binds reversibly to a site in the DDT1 MF-2 cell membranes having pharmacological characteristics of an alpha 1-adrenergic receptor. Following incorporation of (125I)APD into partially purified membranes a single labeled band of protein with a Mr of 81 000 was visualized by autoradiography following sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Incorporation of (125I)-APD into this band was affected by adrenergic agonists and antagonists in a manner consistent with an alpha 1-adrenergic interaction. Prazosin (alpha 1-selective) blocked incorporation of the label into the Mr = 81 000 protein while yohimbine (alpha 2-selective) did not. Of the adrenergic agonists, (-)-epinephrine and (-)-norepinephrine but not (-)-isoproterenol blocked labeling of the Mr = 81 000 protein. We conclude that the ligand binding site of the DDT1 MF-2 cell alpha 1-adrenergic receptor resides in a Mr = 81 000 protein.

Characterization of (3H)-spiperone binding to alpha 1-adrenergic receptors in a smooth muscle cell line

Although (3H)-spiperone has been demonstrated to interact at both dopamine (D2) and serotonin (S2) receptors, it remains a popular choice for characterization of the D2-receptor using both in vitro and in vivo and in vivo assay techniques. Using a clonal smooth muscle cell culture line (DDT1 MF-2), which has previously viously been characterized as possessing alpha 1- and beta 2-adrenergic receptors, we have found that (3H)-spiperone also has a significant affinity for alpha 1-adrenergic receptors. Our results are consistent with other literature reports which have suggested that spiperone may interact at alpha 1-receptors and we have characterized this interaction. We have also found an additional, high affinity binding site for spiperone on these cells which may represent a D2 - receptor. Characterization of this high-affinity site has been difficult since it is present in very low density. We conclude that (3H)-spiperone binds with high affinity to at least three known neurotransmitter receptor sites: D2-dopamine, S2-serotoninn and alpha 1-adrenergic. The binding to the alpha 1-adrenergic receptor exhibits stereospecificity and a considerable degree of similarity in pharmacological profile to the D2-dopamine receptor.

Vasopressin receptor subtypes in dorsal hindbrain and renal medulla

We have investigated the ability of a series of synthetic vasopressin analogues and related peptides to compete with (3H)-arginine8 vasopressin for binding sites in rat renal medulla and dorsal hindbrain. In renal medulla, arginine8 vasopressin and deamino arginine8 vasopressin, a selective antidiuretic, were equipotent while two antagonists of the pressor action of arginine vasopressin were less potent. In the dorsal hindbrain, arginine8 vasopressin and the pressor antagonists were more potent than the synthetic antidiuretic. Potency profiles of these and other analogues suggest that the renal medulla and dorsal hindbrain vasopressin receptors represent different subtypes.

Characterization of a beta-adrenergic receptor in porcine trachealis muscle

To establish a model of airway smooth muscle function we studied binding of [3H]dihydroalprenolol [( 3H]DHA), a beta-adrenergic antagonist, to membrane preparations of porcine trachealis muscle and investigated the response of adenylate cyclase to l-isoproterenol in tissue and plasma membranes. [3H]DHA binding was of high affinity (Kd = 1.0 +/- 0.1 nM), was saturable (Bmax = 87.6 +/- 13.2 fmol/mg protein), and was 90% beta 2 and 10% beta 1. Adenylate cyclase activity in the membrane preparation was (in pmol.10 min-1.mg protein-1 +/- SE): basal 420 +/- 74, guanosine 5'-triphosphate (GTP) (10 micron) 600 +/- 45, GTP (10 microM) + l-isoproterenol (100 microM) 660 +/- 63, NaF (10 mM) 1,500 +/- 134, and forskolin (100 microM) 3,000 +/- 410. Guanosine 5'-diphosphate (GDP) and GTP were active cofactors; l-isoproterenol appeared to function as an effector exchanging GTP for GDP on the guanine nucleotide regulatory protein. There was close agreement of the effective dose (ED50) of the l-isoproterenol-induced relaxation (0.95 +/- 0.45 microM) and the inhibitory constant of l-isoproterenol binding (0.39 +/- 0.10 microM). l-Isoproterenol (100 microM) induced a 100% increase in adenosine 3',5'-cyclic monophosphate (cAMP) levels in tissue strips over basal activity. Investigation of the difference in adenylate cyclase activity between tissue and plasma membranes revealed that l-isoproterenol responsive adenylate cyclase was diminished after initial homogenization. Electron microscopy demonstrated disruption of all cells at this early stage of preparation. The decrease in l-isoproterenol responsive adenylate cyclase following cell rupture is different from other tissues and suggests a difference in the actions of beta-agonist in smooth muscle compared with other tissues.

Autocrine regulation of growth: II. Glucocorticoids inhibit transcription of c-sis oncogene-specific RNA transcripts

The ductus deferens smooth muscle tumor cell line (DDT1MF-2) expresses c-sis proto-oncogene poly A+ RNA transcripts which are thought to encode at least one subunit of the potent mitogen platelet derived growth factor (PDGF). We have previously demonstrated that glucocorticoids block DDT1MF-2 cells in G0/G1 stage of the cell cycle, and that exogenously applied PDGF reinitiates cell cycle progression. In this paper we document that glucocorticoids act to inhibit cell cycle progression by inhibiting the expression of c-sis poly A+ transcripts, which we suggest are encoding a PDGF-like molecule for DDT1MF-2 cells.

Localization and characterization of vasopressin-binding sites in the amygdala of the rat brain

Putative receptors for arginine-vasopressin (AVP) in rat brain were localized and characterized using autoradiographic and radioligand-binding techniques. When brain slices were incubated with tritium-labeled vasopressin, an intense concentration of binding sites was identified which included the medial aspects of the amygdala. Binding of labeled AVP to membrane preparations from this brain region was saturable, specific, reversible, and of high affinity. An antagonist of the peripheral pressor activity of vasopressin was found to be a potent competitor for binding to this site.

Characterization and localization of 3H-arginine8-vasopressin binding to rat kidney and brain tissue

Anatomic, behavioral and pharmacologic evidence suggests that arginine8-vasopressin (AVP) serves as a CNS neurotransmitter or neuromodulator. We have characterized AVP binding to membrane and tissue slice preparations from brain and kidney, and examined the anatomical distribution of these binding sites. Conditions for the binding assay were optimized using kidney medullary tissue. Binding of 3H-AVP (S.A. = 30-51 Ci/mmol, NEN) to brain and kidney membranes and tissue slices was saturable, temperature dependent, linearly related to protein concentration (or number of tissue slices), reversible, and specific since the ability of cold AVP to displace 3H-AVP from binding was greater than oxytocin and other related peptide fragments. Autoradiographic localization of 3H-AVP binding was restricted to kidney medullary tissue. In brain tissue, 3H-AVP binding was found to occur in concentrated foci. Brainstem areas such as the nucleus tractus solitarius (NTS) showed a high density of AVP binding sites. Since local injections of AVP into the NTS have been shown to influence blood pressure, the present study presents the first anatomical evidence for the presence of AVP specific binding sites which might mediate this effect.

Characteristics of an adenylate cyclase coupled beta 2-adrenergic receptor in a smooth muscle tumor cell line

We have shown that binding of 3H-dihydroalprenolol ( [3H] DHA) to DDT1 MF-2 cells and cell membranes was of high affinity, saturable, stereoselective and reversible. The [3H]DHA dissociation constants were 0.63 +/- 0.15 nM (n = 6) and 0.83 +/- 0.04 nM (n = 5) for intact cells and cell membranes, respectively, with a binding site concentration for cells of 27,300 +/- 5,200 sites/cell (n = 6) and for membranes 468 +/- 24 fmoles/mg protein (n = 5). The order of agonist competition for the [3H]-DHA binding site of DDT1 cell membranes was isoproterenol (Ki = 0.20 +/- 0.07 microM) greater than epinephrine (Ki = 0.4 +/- 0.2 microM) greater than norepinephrine (Ki = 66.5 +/- 5.15 microM) consistent with a beta 2-adrenergic receptor interaction. Zinterol, a beta 2-selective antagonist, (Ki = 0.05 +/- 0.01 microM) was 18X more effective than metoprolol, a beta 1-selective antagonist (Ki = 0.9 +/- 0.1 microM), in competing for the DHA binding site. A nonlinear iterative curve fitting analysis of zinterol and metoprolol binding isotherms indicated that (p greater than 0.05) DDT1 cells possess a pure population of beta 2-adrenergic receptors. Finally, we have shown that DDT1 MF-2 cell beta 2-adrenergic receptor is functionally coupled to adenylate cyclase via a G/F protein complex as demonstrated in part by a guanine nucleotide requirement for isoproterenol stimulation of adenylate cyclase activity. In addition, guanine nucleotide mediated a reduction in the affinities of isoproterenol and epinephrine for the [3H]DHA binding site.

Blockade of alpha-adrenergic receptors by analogues of phosphatidylcholine

The experimental evidence reviewed in this article suggests that the kidneys may have an additional function in regulating blood pressure besides their role in controlling both blood volume by urine formation and the relative state of vasoconstriction by the renin-angiotensin system. That is, the kidneys may have an additional influence upon the vasculature of a hormonal vasodilating system. The interstitial cells of the renal medulla appear to be mediating this activity and lipid compounds have been extracted from the renal medulla which display depressor activity. One such compound, the antihypertensive polar renomedullary lipid (APRL), has been demonstrated to consist of specific alkyl ether analogues of phosphatidylcholine. The vascular responses to these compounds include vasodilation of both arterioles and venules, rapid lowering of arterial blood pressure with little or no tachycardia, increased depressor activity in hypertensive animals, and blockade of vascular smooth muscle alpha 1-adrenergic receptors. Most recently, APRL and a synthetic analogue, 1-0-octadecyl-2-acetyl-sn-glycero-3-phosphorylcholine, have been used to demonstrate alpha-adrenergic receptor blockade on a smooth muscle cell line (DDT1) by radioligand assays. This action may be due to the insertion of these compounds into cell membranes causing subsequent steric interactions and blockade of the alpha-adrenergic receptor.

Characterization of the alpha 1-adrenergic receptor subtype in a smooth muscle cell line

We have identified in the DDT1 smooth muscle cell line a [3H]dihydroergocryptine-binding site having the characteristics of an alpha 1-adrenergic receptor. Specific binding of [3H]dihydroergocryptine to DDT1 cells grown either in monolayer or suspension culture was reversible, saturable, and of high affinity, and the binding site demonstrated stereoselectivity. [3H]Dihydroergocryptine dissociation constants of 1.4 +/- 0.2 nM and 1.4 +/- 0.3 nM were observed for suspension and monolayer cells, respectively. However, the concentration of binding sites in suspension-cultured cells (65,100 +/- 8,300 sites/cell) was significantly greater (p less than 0.001) than that found in monolayer cells (27,900 +/- 4,300 sites/cell). The order of agonist competition for the binding site was epinephrine (Ki = 0.92 +/- 0.32 microM) greater than or equal to norepinephrine (Ki = 2.2 +/- 1.0 microM) greater than isoproterenol (Ki = 137 +/- 17 microM), consistent with an alpha-adrenergic interaction. Results of competition experiments with specific antagonists prazosin (alpha 1-selective) or yohimbine (alpha 2-selective) and a computer modeling technique indicated that the alpha-adrenergic receptor of the DDT1 cell was predominantly (greater than 95%) the alpha 1-subtype.

Identification of beta-adrenergic receptors using [3H]dihydroalprenolol in fetal sheep heart: direct evidence of qualitative similarity to the receptors in adult sheep heart

The fetal sheep heart responds to beta-adrenergic stimuli; however, in vivo studies show the response of the fetal heart is less than that of the adult heart. We used [3H]dihydroalprenolol (DHA) to study directly beta-adrenergic receptors in heart particulates of fetal sheep at term and adult sheep. [3H]DHA binding to fetal heart particulates was rapid, reversible (t 1/2 = 2.9 +/- 0.3 min), stereoselective, saturable (101.2 +/- 7.4 fmoles/mg protein), and of high affinity (4.8 +/- 0.4 nM). The rank order of agonists competing for [3H]DHA binding was isoproterenol (0.32 +/- 0.10 microM) greater than epinephrine (1.19 +/- 0.23 muM) approximately equal to norepinephrine (2.67 +/- 0.69 muM), which is compatible with beta 1-adrenergic potencies. [3H]DHA also bound to the adult sheep heart in a manner expected for beta 1-receptors. No difference in the binding affinity of [3H]DHA or agonists' competition was demonstrated between the fetal and adult sheep heart. Comparison of the concentration of beta-adrenergic receptors in fetal and adult hearts was confounded by the choice of the denominator for unit expression. The concentration was higher in the adult when expressed as a function of protein content or 5'-nucleotidase activity (0.52 +/- 0.07 versus 1.12 +/- 0.06). However, there was no difference when tissue weight, Na+ - K+-ATPase, or NaF-stimulated adenylate cyclase was used. Furthermore, isoproterenol-stimulated adenylate cyclase and cardiac contractile response to a threshold dose of isoproterenol were identical in the fetal and adult sheep heart. We conclude that beta-receptors can be studied with [3H]DHA in the fetal sheep heart, this receptor is qualitatively similar to the beta-receptor in the adult sheep heart, and it is unlikely that there is a difference in the concentration of beta-adrenergic receptors in fetal and adult sheep heart.

alpha 1-Adrenergic receptors of a smooth muscle cell line: guanine nucleotides do not regulate agonist affinities

Using [3H]-dihydroergocryptine, we have identified in membranes prepared from the DDT1 MF-2 smooth muscle cell line a binding site with characteristics of the alpha 1-adrenergic receptor. Specific binding (90-95% of total binding) was saturable with a binding site concentration of 197 +/- 44 fmol/mg protein and was of high affinity with a dissociation constant of 1.7 +/- 0.4 nM. The order of agonist competition for the binding site was epinephrine (Ki = 2.3 +/- 0.5 microM) greater than or equal to norepinephrine (Ki = 4.4 +/- 1.3 microM) much greater than isoproterenol (Ki = 195.5 +/- 27.6 microM), consistent with an alpha-adrenergic interaction. Computer modelling of competition curves obtained with prazosin (alpha 1-selective) and yohimbine (alpha 2-selective) indicated that the DDT1 cell alpha-adrenergic receptor was predominantly (greater than 95%) of the alpha 1-subtype. Guanine nucleotides, either GTP or 5'-guanylylimidodiphosphate, did not reduce the affinity of either epinephrine of phenylephrine for the [3H]-dihydroergocryptine binding site.

Decreased concentration of myocardial alpha-adrenoceptors with increasing age in foetal lambs

Using [3H]-dihydroergocryptine, we identified myocardial alpha-adrenoceptor binding sites in foetal lambs and demonstrated that the concentration of receptors decreased with increasing foetal age. The presence of the receptor in the foetus correlated with the presence of myocardial alpha-adrenergic responsiveness. However, we found neither the alpha-receptor binding site nor responsiveness to alpha-adrenoceptor stimulation in the myocardium of adult sheep.

9-AAP, a fluorescent beta-adrenergic antagonist, enters the hamster sperm acrosome in a manner inconsistent with binding to beta-adrenergic receptors

We have previously shown that the hamster sperm acrosome reaction, an event essential for fertilization, is stimulated by beta-adrenergic agonists and inhibited by beta-adrenergic antagonists. In the present report, we describe attempts to use (+/-)-9-aminoacridylpropranolol (9-AAP), a fluorescent derivative of a potent beta-adrenergic antagonist, to microscopically detect beta-adrenergic receptors on cauda epididymal hamster spermatozoa in vitro. 9-AAP binding to washed hamster spermatozoa was localized primarily in the acrosomal region, but we were unable to consistently displace the 9-AAP with the biologically active (-)-stereoisomers of several beta-adrenertic agonists and antagonists. Such displacement is necessary in order to separate binding to receptors from "nonspecific binding." Thus we did not detect sperm beta-adrenertic receptors by this method. Failure to detect the receptors with 9-AAP may be due to their presence in numbers too low for detection by this compound or to the masking of the receptors in these uncapacitated sperm. However, we could displace 9-AAP with either 5.0 mM NH4Cl or 1.2 microgram/ml nigericin, compounds capable of discharging pH gradients across cell membranes. These compounds have also been previously reported to displace the fluorescent portion of 9-AAP, 9-aminoacridine from the acrosome by such mechanism. The present results suggest that 9-AAP fluorescence does not always represent binding to beta-adrenergic receptors or "nonspecific binding," but may also represent the concentration of 9-AAP in acidic compartments within a cell.

Stimulation of in vitro activation and the acrosome reaction of hamster spermatozoa by catecholamines

Capacitation and the acrosome reaction of mammalian spermatozoa are essential for fertilization. In vitro results are presented that demonstrate that catecholamines stimulate activation (a whiplash flagellar movement characteristic of capacitated hamster spermatozoa) and the acrosome reaction. Protein-free ultrafiltrates of bovine adrenal cortex and medulla preparations stimulated motility, activation, and acrosome reactions of hamster spermatozoa in the presence of bovine serum albumin. The medulla preparation was more effective than the cortex preparation in the stimulation of activation and acrosome reactions. Epinephrine (0.5-50 muM) and norepinephrine (50.0 muM) in the presence of bovine serum albumin and a partially purified protein-free cortex preparation also stimulated activation and the acrosome reactions. Both activation and acrosome reactions in the presence of epinephrine were inhibited by the adrenergic antagonists phentolamine and propranolol, suggesting the involvement of alpha- and beta-adrenergic receptors in the stimulation of capacitation and the acrosome reaction. In addition, phenylephrine, an alpha-adrenergic agonist, was as potent as epinephrine in the stimulation of acrosome reactions, but activation was reduced. Isoproterenol, a beta-adrenergic agonist, was as potent as epinephrine in the stimulation of activation, but acrosome reactions were reduced. High percentages of both activation and acrosome reactions were observed only in the presence of epinephrine, norepinephrine, or phenylephrine and isoproterenol together.